Recovery of Excessive NH_3 in Black Liquor from NH_4OH-KOH Pulping of Wheat Straw |
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| Authors: | HUANG Guo-lin CHEN Zhong-sheng ZHANG Kai Key Laboratory of Nuclear Resources Environment Ministry of Education East China Institute of Technology Jiangxi China |
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| Institution: | Key Laboratory of Nuclear Resources and Environment, Ministry of Education, East China Institute of Technology,Jiangxi 344000, China |
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| Abstract: | Aqueous ammonia mixed with caustic potash as wheat straw pulping liquor was investigated. The caustic potash not only reduced the NH3 usage and cooking time, but also provided a potassium source as a fertilizer in the black liquor. Excessive NH3 in black liquor from wheat straw NH4OH-KOH pulping process was recovered by batch distillation with a 98% recovery rate of free NH3 under atmospheric pressure and constant reflux. The temperature at the bottom of the column was controlled at 104 - 105 ℃. After removal of free NH3, the black liquor contained 8.4 g/L NH3-N and 7. 04 g/L total potassium, with a substantial amount of ammoniacal lignin, and it could be used as a liquid fertilizer for farming. The height equivalent to a theoretical plate (HETP) of a rectifier for recovering free NH3 was calculated. The diameter and height of packing of the rectifier based on a daily consumption of 75 t oven-dry wheat straw were estimated. |
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| Keywords: | NH4OH-KOH pulping excessive NH3 distillation recovery |
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